It is known that derivatives of polyalkylpiperidines, and specifically those that are substituted in the 4-position, are very effective light stabilizers for coatings and plastics. Examples of such compounds are the ethers, esters and carbamates of 2,2,6,6-tetraalkylpiperidine-4ols, such as described in U.S. Pat. Nos. 4,056,507; 4,089,842; 4,219,464; 4,226,999; 4,234,734 and 4,311,820. Some types of polyalkylated 4-amino piperidine derivatives are disclosed in U.S. Pat. Nos. 3,684,765; 4,166,813 and 4,316,837. Still other types of light stabilizers containing the polyalkylpiperidine radical have a variety of 4-substituents as disclosed in U.S. Pat. Nos. 4,265,803; 4,299,926; 4,312,804 and 4,319,030.
It is well known in the art that while the polyalkylpiperidine radical is effective as a light stabilizer for synthetic polymers, low molecular weight piperidine derivatives are relatively volatile and are thus subject to migration out of the coating or plastic, particularly during processing. In some instances these stabilizers can be easily extracted from the synthetic polymers with water or with organic solvents making them of little practical use for the stabilization of synthetic polymers. Most of the patents cited above represent attempts to overcome these problems by making higher molecular weight and especially polymeric derivatives of polyalkylpiperidines. In general, the capacity for migration and the extractability of the stabilizer do indeed fall as molecular weight increases but, on the other hand, the compatibility of the stabilizer, particularly polymeric stabilizers, with the synthetic polymer to be protected also decreases. This compatibility is, however, dependent not only on the molecular weight of the stabilizer but also on its chemical structure and the nature of the synthetic polymeric substrate to be protected.